Thermographic copying material



United States Patent Ofifice 3,342,618 Patented Sept. 19, 1967 3,342,618 THERMOGRAPHIC COPYING MATERIAL Warner L. Peticolas, San Jose, Calif., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Dec. 31, 1962, Ser. No. 248,308 14 Claims. (Cl. 117-367) The present invention generally relates to image duplication and more particularly relates to an improved thermographic copying medium, to a method of making the improved copying medium and to an improved method of thermographic copying.

A wide variety of systems exist for image duplication, particularly for copying or duplicating printed material and the like. Some of such systems employ so-called wet techniques. One such wet system employs a photo-sensitive paper as its basic element. A latent image is formed on the paper upon exposure to light in contact with the material being copied. The latent image is then developed in a suitable solution and is transferred to another paper sheet which is placed in contact with the image-carrying wet sheet, so that a suitable duplication of the original image is obtained. The second sheet must then be dried before use. This system has found extensive use in some business operations and is capable of providing clear, relatively detailed duplicate images.

However, there are certain disadvantages in most wet ty-pe copying systems, including the fact that they require periodic addition or replacement of the developing solution. A relative large number of manual steps are usually required. Moreover, the operator must handle damp paper materials, and there is a certain drying time required after the duplicate image is prepared before the copy paper can be effectively utilized. Furthermore, most of the wet type system duplicating methods are relatively time consuming and expensive, so that reproduction costs can amount to as much as ten cents or more a copy.

Accordingly, several simpler, less expensive thermographic copying systems have been devised, as well as more expensive systems using xerographic techniques. These less expensive systems eliminate the use of solutions and rely solely upon the application of heat to thermosensitive paper or the like to effect the development of the duplicate image thereon. In most such thermographic copying systems, however, specially prepared relatively delicate and weak papers are required for the copying. Such papers have a tendency to deteriorate relatively rapidly, i.e. have a relatively short shelf life, and are not usually considered to provide permanent copies. Moreover, due to the nature of the copying paper, the reproduced image has a dark background and is relatively unclear. Usually there are no significant color or tone gradations in the duplicate image. Accordingly, while such duplicate images can be reproduced relatively inexpensively, they are generally considered to be relatively unsatisfactory for many purposes. Further, such reproduced images usually cannot be rendered permanent, i.e. resistant to deterioration upon further heating of the duplicate image-carrying paper. In addition, additional copies of the duplicated image usually cannot be made from the copy paper carrying the same.

Accordingly, it is a principal object of the present invention to provide an improved graphic copying method.

It is also an object of the present invention to provide an improved graphic copying medium and method of making same.

It is a further object of the present invention to provide an improved image reproducing method, which method is simple and inexpensive and which produces copies the developed images of which can be readily protected against deterioration.

It is also an object of the present invention to provide an improved method of graphically copying, which method permits further copying of the reproduced image, by a variety of techniques.

It is also an object of the present invention to provide an improved graphic copying medium which has good storage stability, which is relatively inexpensive, and which can be simply treated to permanently protect a developed image.

It is a further object of the present invention to provide a simple, inexpensive dry graphic copying method which eliminates the necessity of using solutions for image reproduction, but which can provide a clear permanent image, capable of being readily reproduced.

It is a still further object of the present invention to provide an improved graphic copying medium which is capable of being used as a master for further image duplication, as in printing processes.

These and other objects are achieved, in accordance with the present invention, by providing an improved thermographic copying medium which can be effectively made from relatively inexpensive materials, a method of making the same, and an improved thermographic copying method employing such improved medium. The improved thermographic copying medium incorporates an effective concentration of an inclusion compound containing host molecules and guest molecules. Inclusion compounds are available in six different forms. One form is known as clathrates, which are produced when guest molecules are held by physical forces within separate enclosed chambers provided within a crystal lattice composed of host molecules. The guest molecules are smaller than the cavities in the crystals of the host molecules in which they reside but not so small as to readily diffuse therefrom. Because the guest molecules are contained within the lattice of the host molecule crystals by mechanical rather than chemical means, they may be of any desired nature, i.e. even inert gases, so long as their diameters are slightly smaller than the diameter of the cavities in the host molecule crystals.

A second form of an inclusion compound is known as a canal complex and is characterized by host crystal lattices having tubular cavities extending therethrough into which guest molecules may be disposed in orderly arrangement. Other types of inclusion compounds include: (A) layer complexes comprising crystals with alternating layers of guest and host molecules; (B) molecular sieves comprising crystals having interconnecting passages in which guest molecules may be disposed; (C) intramolecular hollow space complexes comprising large host molecules with guest molecules in molecule-receiving concavities; and (D) linear polymer complexes in which guest molecules are disposed in hollow tubes formed by pipelike host molecules.

The guest molecules can be released from the inclusion compound, that is, from the crystals of the host molecules upon decomposition of the crystals, as upon heating. In accordance with the present invention, heat sufl'lcient to release the guest molecules at a rate and in amounts suflicient to develop an image in a dispersing medium is applied only to those selected areas of the dispersing medium containing the inclusion compound corresponding to the areas of the image being duplicated. The guest molecules are so selected with respect to the dispersing medium that there is a physical or chemical, or both, development of the desired image. Thus, for example, the guest molecules may be released in the form of gas bubbles which pass up through the medium and disrupt its surface so as to cause selective opacification. The gas bubbles may bulge the surface of the medium so that the image is further reproduced in the form of a raised surface on the medium, from which other duplications can easily be printed or otherwise reproduced. Alternatively, the guest molecules may be selected so that upon their release from the inclusion compound, they chemically react with the dispersing medium in which they are disposed to provide a color change therein and thus effect the desired image duplication.

The inclusion compound is stable at temperatures below those required to release the contained guest molecules. Moreover, the reproduced image can be permanently protected by selective treatment of the dispersing medium, so that subsequent inadvertent application of heat does not impair, destroy or deform the reproduced image.

In one embodiment of the present invention, given by way of example, an acetone solution containing 4% by weight of hydroquinone and 33% by weight of a selected vinylidene chloride thermoplastic resin sold under the trademark Saran and more particularly comprising a resin obtained by polymerization of vinylidene chloride or copolymerization of vinylidene chloride with lesser amounts of unsaturates, was prepared and coated on a suitable plastic substrate comprising polyethylene terephthalate sheeting. The coating was dried thereon in an oven and after drying was clear and transparent. The resultant composite sheet aws then placed in a carbon dioxide atmosphere at 100 C. and 500 p.s.i. to saturate the crystallized hydroquinone with carbon dioxide. Upon cooling of the sheeting while under the indicated pressure, the carbon dioxide was captured within the sheeting. Accordingly, an improved inclusion compound-containing thermographic copying material was produced. The carbon dioxide molecules served as clathrate guest molecules disposed in the crystals formed of hydroquinone molecules. When selected portions of the coating corresponding to an image to be duplicated were exposed to heat, for example at about 95 C., an image was formed in the coating in the following manner: Carbon dioxide molecules were released from the hydroquinone crystal lattice and migrated upwardly through the softened Saran as gas bubbles. The bubbles raised the surface of the Saran in areas duplicating the areas of the image and formed a multitude of small pits or cavities therein. The irregularities in the Saran surface diffracted light so as to produce a bright white opaque image. Since the image was substantially raised above the remaining surface of the Saran, it could be selectively inked and further reproductions of the image could be printed off on paper or the like from the Saran master.

Referring now more particularly to the method of making the improved thermographic copying medium of the present invention, a solid mixture comprising suitable inclusion compound preferably uniformly distributed in a normally solid dispersing medium is formed. The dispersing medium is capable of being reacted with guest molecules of the inclusion compound so that an image is developed or repreduced therein. The inclusion compound can be formed before the uniform distribution in the dispensing medium. Alternatively, a material containing host molecules for the proposed inclusion compound can be uniformly distributed adjacent to the surface of the medium or within the medium, and then the inclusion compound can be formed in situ by introduction of the guest molecules into crystallized host molecules.

The uniform distribution of the inclusion compound in the dispersing medium, preferably adjacent the surface thereof, can be carried out in any suitable manner. For example, a host molecule-containing material can be dissolved along with the dispersing medium in a vaporizable solvent, as indicated in the previous example, in order to uniformly distribute the same, and then after drying and crystallization of the host molecules the guest molecules can be added. Other methods of uniformly distributing the inclusion compound in the dispersing medium can be used, as by mechanical mixing when the dispersing medium is in a molten condition and the inclusion compound itself is and remains a crystalline solid. Thereafter, the dispersing medium containing the inclusion compound is set to solid form, as by drying, etc.

It will be understood that only certain types of chemicals are suitable for use as inclusion compound host molecules. One such material which forms a clathrate is hydroquinone, otherwise known as quinol or para-dihydroxybenzene, having the generalized chemical formula C H (OH) Hydroquinone is soluble in water, alcohol and ether and has a melting point of 170 C. and a boiling point of 285 C. Hydroquinone readily crystallizes to form a crystalline molecular complex having vacancies therein with radii up to about 2 A. It has been found that, for the purposes of the present invention, molecules which may be used as the guest molecules with the hydroquinone host molecules are those which have radii of less than 2 A. Guest molecules having a radii as small as 1.5 A. can be used. Thus, molecules of carbon dioxide, oxygen, sulfur dioxide, hydrogen sulfide, hydrogen chloride, formic acid, acetonitrile, methyl alcohol, argon and many other substances can be employed as the guest molecules. Mixtures of guest molecules can also be used, i.e. both CO and 0 It will be understood that the guest molecules should be selected so as not to deleteriously affect, upon their release from the inclusion compound, either the dispersing medium or any substrate upon which the dispersing medium may be disposed. The guest molecules may be introduced into the crystalline host molecular complex, such as hydroquinone, by any suitable means, e.g. under pressure at elevated temperature below the melting point thereof. The hydroquinone crystals release the guest molecules at elevated temperature, particularly at the decomposition point of the clathrate which is formed. For rapid release of the guest molecules from the hydroquinone, the hydroquinone can be heated to a temperature of, for example, above 170 C. However, temperatures as low as C. are also suitable for sufficiently rapid release of guest molecules to accomplish image development in the dispersing medium. The guest molecule release temperature will, of course, be selected also with regard to the characteristics of the dispersing medium in which the inclusion compound is disposed.

Pyrocatechol also known as catechol can also be used as the clathrate host molecules. Pyrocatechol is orthodihydroxybenzene, having the same chemical formula as hydroquinone but with a melting point of 104 C. and a boiling point of 245 C. It is soluble in water, alcohol, ether, benzene and chloroform and aqueous alkaline solutions. The same guest molecules can be utilized therewith as previously described for the hydroquinone.

Resorcinol, which is meta-dihydroxybenzene, of the same chemical formula as catechol and hydroquinone but with a melting point of 1l0.7 C. and a boiling point of 281 C. may be used in place of or in addition to hydroquinone and/or catechol in forming the clathrate. Resorcinol is soluble in water, alcohol, ether, glycerol, benzene and other solvents. Again, guest molecules meeting the same criteria as described in connection with the guest molecules for hydroquinone can be used.

Other multi-hydroxy aromatic compounds, for example, the trihydroxybenzenes, pyrogallol and phloroglucinol, can be used as the crystalline host molecule complex.

Water can also be used as a clathrate-forming system, acting in the crystalline state as the host for selected gas molecules. Such clathrates are known as gas hydrates and are usually relatively simple crystals with relatively low melting points. They can be utilized in the present invention for the same purpose as the previously described clathrate systems. They are generally prepared by forcing gas to dissolve in water under pressure and then chilling the solution until it freezes. Thus, the host molecules are water while the guest molecules usually are gases or low boiling point liquids. For example, small molecules such as chlorine, bromine, sulfur dioxide, hydrogen sulfide, methane, ethane, methyl chloride and methlylene chloride can be used. Certain guest molecules of slightly larger diameter can also be used, for example, chloroform, ethyl chloride, methyl iodide, difluorobromochloromethane and propane. Such gas hydrates may melt, for example, at temperatures of, for example, 61 C. and 69 C. in the case of the inclusion of sulfur dioxide and chlorine, respectively, as the guest molecules in the water.

The preceding examples of crystalline host molecule complexes with guest molecule inclusions are ones in which the crystal lattice of host molecules wholly encloses the guest molecules in the manner of, for example, a molecular trap. Instead of such an arrangement, certain host molecule crystalline systems which have tubular cavities therein, within which cavities guest molecules may be disposed in an ordered arrangement, can be used. Such systems are known as canal complexes. Typical of hosts which form canal complexes are urea and thiourea. Urea has the chemical formula CO(NH a melting point of l32.7 C., and decomposes before boiling. Thiourea is generally similar, having the formula (NH CS. It has a melting point of 180-l82 C. and sublimes in vacuum at about l50l60 C. Thiourea is soluble in cold water and alcohol while urea is soluble in water, alcohol and benzene. The crystalline urea complex has a cavity diameter of 5 A. and is capable of accepting straight chain hydrocarbons and fatty acids, for example, hexane and pentane. Hexane and pentane have boiling points of 68.742 C. and 36.074" C., respectively. Thiourea has cavities therein in the crystal structure which are capable of accepting guest molecules having diameters of less than 7 A., particularly selected cycloparaflins and polymethylated or polychlorinated hydrocarbons.

Another representative of the canal complex type of host molecules is desoxycholic acid, otherwise known as deoxycholic acid, having a chemical formula of C H O This is a bile acid with a melting point of 172l73 C. It is practically insoluble in water and benzene but freely soluble in alcohol and acetone and in solutions of alkali hydroxides and carbonates. Deoxycholic acid is capable of accepting fatty acids within the cavities of the canal complex thereof, that is guest molecules which have molecular diameters of less than about 5 A. It will be understood that other types of inclusion compounds can also be successfully employed for the purposes of the present invention.

In selecting particular inclusion compounds, a number of criteria are to be observed. In this regard, the inclusion compound guest molecules must have a diameter which is slightly less but preferably not greatly less than the diameter of the cavity, etc. in the crystal structure of the inclusion compound host molecule or molecule complex cavity. An inclusion compound host must be in the crystalline state at suitable temperatures and must be capable of decomposing or otherwise releasing the host molecules at a suitable temperature. For thermographic copying, the guest molecule release temperature should be sufficiently high so that inadvertent and substantial release of the guest molecules does not occur under normal storage conditions, but should be sufiiciently low so that such release does not require a large heat input. Moreover, the host molecule crystals should have a decomposition point compatible with the softening point of the dispersing medium in which the inclusion compound is to be disposed. In other words, suitable selection of host molecules may be made with respect to the dispersing medium in which the inclusion compound is to be disposed so that in heating the system to develop the latent image the plastic dispersing medium is preferably sufiiciently soft at the time of release of the host molecules to facilitate chemical reaction therewith and/or migration of guest gas bubbles therethrough for production of the desired opacity or color change in the dispersing medium.

Depending upon the particular inclusion compound and dispersing medium, it is not in all instances necessary or desirable that the medium be soft at the time of release of the guest molecules. Thus, in a given instance chemical reaction between the dispersing medium and the guest molecules can be effected even though the medium is in the essentially solid state. Of course, it will be understood that release of the guest molecules from the inclusion compound is usually easier and the desired image-imparting reaction with the dispersing medium is usually more immediate when the medium in the area of guest molecule release is at least soft. The guest molecules may be released in gaseous or non-gaseous form from the inclusion compound and in either form may react, if desired, with the dispersing medium, but in most instances should not react with any subtrate present.

It has been found that for purposes of providing a mechanical image-forming means, certain inclusion com pound guest molecules releasable in gaseous form are more suitable than others. In this connection, it has been found that carbon dioxide usually tends to lubricate plastics and to provide much higher raised areas in thermoplastic media than does nitrogen, for example. Inasmuch as carbon dioxide is innocuous, inexpensive and readily available, it is one of the preferred types of guest molecules. Oxygen is also a preferred gas for similar reasons.

The dispersing medium is one which is normally solid and preferably transparent but also one which can be readily transformed to a softened or molten form, if desired. It has been found, that for most purposes, the dispersing medium will comprise one or a mixture of suitable synthetic resinous thermoplastic materials. It will be understood that the dispering medium need not be transparent if the inclusion compound releases guest molecules which change the appearance of the dispersing medium sufficiently to clearly provide image formation, e.g. change the color thereof, etc. Synthetic thermoplastic resins of the nature of polyvinyl resins, including polyvinyl chloride, and the like, polystyrene and acrylate and methacrylate resins can be utilized. Thermosetting resins, for example, phenol-formaldehyde, polyester and phenolic type resins can also be used with thermoplastic resins. Mixtures of thermoplastic resins can be used, such as a mixture of Saran, a vinylidene chloride polymer, and polymerized methyl methacrylate resin. The resins are selected for their physical and chemical characteristics, including their melting and softening points, preferably their transparency and the like.

The dispersing medium may be utilized in the form of a sheet of extended surface area, with or without a suitable substrate, such as clear plastic or paper, if transparency is not desired, etc., to which it firmly adheres. As an example, a dispersing medium comprising a mixture of Saran and polymethyl methacrylate and containing hydroquinone in a solvent may be applied as a thin wet coating to a substrate of polyethylene terephthalate resin (commercially known under the registered U.S. Trademark Mylar of E. I. Du Pont de Nemours Co., Wilmington, Delaware), and then dried by solvent evaporation. Carbon dioxide host molecules may then be added to the hydroquinone. Mylar has a melting point of 265 C., while the Saran has a softening point of about 70-175 0, depending upon the extent of polymerization; methyl methacrylate polymer also has a comparably low softening point. A coating material comprising a mixture of the Saran and polymethyl methacrylate resins softens at a lower temperature than the substrate of Mylar.

It will be understood, however, that if desired the material upon which the coating of dispersing medium can be disposed may itself comprise a dispersing medium. Once the coating of dispersing medium is dried and the giest molecules have been introduced thereunto, as previously described, the product is ready for use as an improved thermographic copying material. Thus, the specially coated plastic films, papers and the like containing inclusion compounds adjacent the surface thereof provide improved thermographic copying media in accordance with the present invention. Such coatings may be relatively thin and still provide desired results. Thus, coating thicknesses of, for example, from a few thousandths to several tenths of an inch can be successfully employed, as can other thicknesses of the dispersing medium.

The thermographic copying method of the present invention comprises selectively heating those areas of the inclusion compound-containing copying medium corresponding to the areas of an image to be copied, as by passing infrared radiation through juxtaposed image-containing material and thermographic copying medium. The heating is carried out to above the decomposition point of the inclusion compound so that the guest molecules in the inclusion compound react chemically a'nd/or physically with the copying medium to reproduce the desired image in the copying medium.

For example, the original copy is positioned closely adjacent or in surface contact with the inclusion compound-containing copying medium. Next, the original copy side is exposed to radiation, such as from an infrared lamp, which is substantially reflected or dissipated by the light or non-printed areas of the original copy and substantially absorbed by the materials forming the dark or printed areas of the original copy and thereby converted into heat. The heat generated in such radiated areas is sulficient to cause decomposition of the inclusion compound and the release of the guest molecules thereby disrupting the copying medium and reproducing the printed areas of the original copy.

Once the image is formed in the surface of the thermographic copying medium, such image can be protected against deterioration by maintaining the image-free areas of the thermographic copying medium at temperatures below those which would cause release of more than negligible amounts of the guest molecules. This can be accomplished by storing the exposed copying medium in a cool location or by coating the image-free areas of the copying medium with suitable heat insulating means, if desired. However, particularly in the case where the guest molecules form gas bubbles and react physically with the dispersing medium to raise the surface thereof and opacify the same, a more effective method of protecting the imagecarrying thermographic copying medium is to subject it to a controlled temperature which causes a controlled but slow release of guest molecules from the image-free areas thereof, the rate of such release being insufficient to substantially opacify the dispersing medium and substantially bulge or raise the surface thereof. Thus, for example, a carefully controlled baking operation which causes release of a very small percentage of the guest gas molecules per unit time, for example about 1% per minute in the image-free areas, will result in essentially complete depletion of the guest gas, for example carbon dioxide, from a hydroquinone-carbon dioxide inclusion compound system in Saran or the like without producing an image and without adversely affecting the already-formed image. It will be understood that other means can be employed for making permanent the image formed in the thermographic copying medium. The image-containing areas are, of course, permanent in and of themselves. Methods of preserving the formed image depend upon keeping the remaining areas of the thermographic copying material image-free.

The following example further illustrates certain features of the present invention.

EXAMPLE An acetone solution was prepared which contained 4% by weight of hydroquinone and 33% by weight of a commercially available vinylidene chloride polymer (Saran 220) having a melting point of 90 C. This solution was coated to about 1 mil thickness upon a polyethylene terephthalate base about 3 mils thick. The film was then placed in an oven and dried at 125 C; to provide a clear, dry, transparent coating on the base sheet. The sheets were then placed in a pressure vessel and heated to 100 C. in CO at 500 p.s.i. After 5 minutes the vessel was then slowly cooled to ambient temperature while maintaining the CO at about the initial pressure. The cooling was carried out over a period of about an hour. During the cooling in the presence of the C0 C0 molecules became captured in the hydroquinone crystal lattice to form a clathrate.

The thus prepared thermographic copying material was placed against a sheet of paper containing printing and infrared radiation was then passed through the copying material and was selectively reflected back thereto from the printed sheet. This was accomplished by passing the juxtaposed paper sheet and copying material through a thermographic copying machine set at C.

Those areas of the coating of the copying material corresponding to the printed areas of the paper sheet were heated sufiiciently so that the dispersing medium was softened and the carbon dioxide molecules were released from the hydroquinone therein, causing the dispersing medium to opacify. The opacification was due to the upward passage of carbon dioxide bubbles to the surface of the dispersing medium, causing a pitting and raising of the surface. The multitude of fine pits in the raised area effected light diffraction and provided a bright white opaque image.

The copying material was then cooled to ambient temperature to set the raised spongy opaque areas. The copying material was then placed in an oven and baked at 75 C. for a period of 10 minutes until the carbon dioxide contained in the image-free areas thereof was substantially completely driven off at a sufiiciently slow rate to prevent opacifying and raise the surface of the dispersing medium.

Thereafter, the copying material was removed from the baking oven, the raised letters in the dispersing medium were inked and copies of this master were then printed off onto sheets of paper. Clear, sharp images were produced both in the thermographic copying material itself and in the copies printed therefrom.

The preceding example clearly illustrates an improved thermographic copying medium which can be simply and inexpensively made and which is capable of being readily utilized in an improved method of thermographic copying. The thermographic copying medium can be fabricated utilizing a wide variety of inclusion compounds depending on the particular use to be made of the same. A large number of dispersing media and substrates can also be employed for the copying medium. The copying method does not require the use of solutions or complicated procedures for the development of an image therein, but only relatively low treating temperatures. The image can be produced by physical and/or chemical action and can be opaque white, raised and spongy, if desired. The imagecontaining thermographic copying medium can be used for printing reproductions of the clear, sharp image obtained, and such image can be made permanent in a simple and effective manner. The thermographic copying medium is suitable for use in the copying of pictures as well as printing. Moreover, the thermographic copying medium is storage stable and convenient to use. Further advantages of the present invention are as set forth in the foregoing.

While there have been described above and illustrated various alternative steps of providing an improved thermographic copying medium and a method of utilizing the same, all modifications, variations and alternative steps falling within the scope of the appended claims are part of the invention.

What is claimed is:

1. An improved thermographic copying method, which method comprises:

selectively heating areas, corresponding to the areas of an image to be copied, of a copying medium comprising a film of organic resinous film-forming material having uniformly dispersed therein inclusion compounds of host molecules containing guest molecules, said inclusion compounds being decomposed by heat to release the guest molecules from the host molecules, said guest molecules being capable of disrupting said film upon release from the host molecules,

only said heating in the selected areas being carried out above the decomposition point of said inclusion compounds to cause the release of said guest molecules and thereby disruption of the film-forming material to form the image in the copying medium.

2. An improved thermographic copying method, which method comprises positioning an image-carrying medium adjacent a thermographic copying medium containing inclusion compounds, host molecules containing guest molecules, substantially uniformly distributed in a transparent film of organic resinous film-forming material,

said inclusion compounds being disposed by heat to release the guest molecules capable of being released as a gas and capable of disrupting said transparent film to opacify the same,

exposing said image-carrying medium to radiation absorbed by the image and converted to heat sufiicient when transferred to said copying medium to be above the softening point of said film and above the decomposition point of said inclusion compounds only in those areas of the film that correspond to the image to be reproduced so as to cause the release of said guest molecules at a rate and in amounts sufficient to disrupt the film and opacify the same and thereby reproduce said image therein,

said guest molecules bubbling up through said softened film and causing the surface of the film affected thereby to rise and to become pitted,

whereby light contacting the raised areas is diffracted and a bright white image is produced.

3. The method of claim 2 wherein said inclusion compounds are clathrates containing normally gaseous guest molecules, and wherein said film comprises normally transparent synthetic thermoplastic resin.

4. The method of claim 3 wherein said clathrates comprise crystalline hydroquinone containing carbon dioxide guest molecules, wherein said synthetic thermoplastic resin includes vinylidene chloride polymer, and wherein said chloride polymer is disposed as a solid coating on a solid transparent polyethylene terephthalate substrate.

5. An improved thermographic copying medium comprising a normally solid film of organic resinous filmforming material and inclusion compounds substantially uniformly distributed adjacent a surface of said film,

said inclusion compounds comprising clathrates formed of crystalline hydroquinone host molecules containing carbon dioxide guest molecules, said clathrates being decomposed by heat to release the carbon dioxide guest molecules from the crystalline hydroquinone host molecules, said carbon dioxide guest molecules being capable of disrupting said film upon release from the crystalline hydroquinone host molecules,

said film comprising a synthetic thermoplastic vinylidene chloride polymer and is disposed as a solid coating on the surface of a transparent synthetic polymeric substrate having a higher softening point than said film.

6. The improved thermographic copying medium of claim 5 wherein said inclusion compound-s comprise clathrates formed of crystalline hydroquinone containing carbon dioxide guest molecules,

wherein said synthetic thermoplastic resin polymer comprises vinylidene chloride polymer and wherein said film is disposed as a solid coating on the surface of a transparent synthetic plastic polymeric substrate having a higher softening point than said film, said substrate comprises polyethylene terephthalate film. 7. The method of making an improved thermographic copying medium, which method comprises substantially uniformly distributing material containing host molecules for inclusion compounds in an organic resinous film-forming material and introducing into the resulting host molecule-containing material gaseous guest molecules to form in situ inclusion compounds, said inclusion compounds being capable of releasing said guest molecules therefrom upon heating, said guest molecules being capable of disrupting filmforming material. 8. The method of making an improved thermographic copying medium, which method comprises,

substantially uniformly distributing in the liquid state material containing host molecules for inclusion compounds in a liquified normally solid organic resinous film-forming material, setting the resultant mixture to form a solid film and thereafter introducing into the resultant crystallized host molecule-containing material gaseous guest mol ecules to form inclusion compounds in situ, said guest molecules being releasable from said inclusion compounds upon heating thereof and being capable of disrupting said film, said dispersing medium having a softening point below the temperature at which image-forming amounts of guest molecules are releasable from said inclusion compounds, said film being transparent, and said guest molecules being releasable from said inclusion compounds as gas capable of physically disrupting said film to opacify the same. 9. The method of making an improved thermographic copying medium, which method comprises substantially uniformly distributing in the liquid state material containing host molecules for inclusion compounds in a liquified normally solid organic resinous film-forming material, setting the resultant mixture to form a solid film and thereafter introducing the resultant host moleculecontaining material guest molecules "to form inclusion compounds in situ, said guest molecules being releasable from said inclusion compounds upon heating thereof and being capable of reacting with said dispersing medium to develop an image therein, said dispersing medium having a softening point below the temperature at which said guest molecules are releasable from said inclusion compounds, said film being transparent, said inclusion compounds comprising clathrates and said film comprising synthetic thermoplastic resin polymer, said clathrates comprising crystallized hydroquinone containing carbon dioxide guest molecules capable of disrupting said film to opacify the same, said film comprising vinylidene chloride polymer, said film being disposed as a coating on a transparent substrate comprising polyethylene terephthalate film. 10. The method of making an improved thermographic copying medium, which method comprises,

substantially uniformly distributing crystalline inclusion compounds in a liquified normally solid transparent organic resinous film-forming material, said inclusion compounds containing guest molecules releasable there-from as gas upon heating and capable of disrupting said film to opacify the dispersing medium and raise the surface thereof, and setting the resultant mixture to form a solid film while maintaining the inclusion compounds in crystalline form,

said inclusion compounds comprising clathrates, and

said film-forming material comprising synthetic thermoplastic resin polymer,

said clathrates comprising crystallized hydroquinone containing carbon dioxide guest molecules, said film-forming material comprising vinylidene chloride polymer,

said film-forming material being disposed as a coating on a transparent substrate comprising polyethylene terephthalate film.

11. An improved thermographic copying method comprising: selectively heating areas of a copying medium comprising a film of organic resinous, film-forming material having uniformly dispersed therein inclusion compounds of host molecules containing guest molecules, said inclusion compounds being decomposed by heat to release the guest molecules from the host molecules, said guest molecules being capable of disrupting said film upon release from the host molecules, only said heating in the selected area being carried out at a temperature near the softening point of the film-forming material and above the decomposition temperature of the inclusion compound and for a time sufficient to cause the release of the guest molecules in a gaseous state and in a sufficient amount such that said layer is disrupted in the heated areas and an image is produced therein.

12. An improved thermographic copying method comprising:

positioning an image-carrying medium adjacent a copying medium comprising a film of organic resinous film-forming material having inclusion compounds, of host molecules containing guest molecules substantially uniformly distributed at about the surface thereof, said inclusion compounds being decomposed by heat to release the guest molecules from the host molecules, said guest molecules being capable of disrupting the film upon release from the host molecules,

exposing said image-carrying medium to radiation absorbed by the image and converted to heat sufficient When transferred to said copying medium, the softening point of said film and above the decomposition point of said inclusion compounds only in those areas of the film that corresponding to the image to be reproduced so as to cause the release of said guest molecules at a rate in an amount sufiicient to disrupt the film-forming material of the copying medium, thereby reproducing the image of said image-carrying medium.

13. The method of claim 12 wherein after said image is formed in the copying medium, heating the copying medium to a temperature Which affects the release of said guest molecules from the image-free areas thereof in amounts and at a rate insuflicient to affect said image and maintains that temperature until substantially all of said guest molecules have been released from said imagefree areas.

14. The method of claim 12 wherein said inclusion compounds are selected from the group consisting of clathrates and canal complexes.

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2,916,622 12/1959 Nieset 117-36.8 X 2,993,805 7/1961 Kay 117-36.7 X 3,018,264 1/1962 Colcough 2602 3,080,254 3/1963 Grant 11736.8 3,108,872 10/1963 McMahon 11736.7 X 3,158,480 11/1964 Adkisson et al. 11736.7 X 3,171,734 3/1965 Peticolas l1736.7 X 3,244,354 12/1965 Dietzgen et al. 11736.8 X

DAVID KLEIN, Primary Examiner. 

1. AN IMPROVED THERMOGRAPHIC COPYING METHOD, WHICH METHOD COMPRISES: SELECTIVELY HEATING AREAS, CORRESPONDING TO THE AREAS OF AN IMAGE TO BE COPIED, OF A COPYING MEDIUM COMPRISING A FILM OF ORGANIC RESINOUS FILM-FORMING MATERIAL HAVING UNIFORMLY DISPERSED THEREIN INDLUSION COMPOUNDS OF HOST MOLECULES CONTAINING GUEST MOLECULES, SAID INCLUSION COMPOUNDS BEING DECOMPOSED BY HEAT TO RELEASE THE GUEST MOLECULES FROM THE HOST MOLECULES, AID GUEST MOLECULES BEING CAPABLE OF DISRUPTING SAID FILM UPON RELEASE FROM THE HOST MOLECULES, ONLY SAID HEATING IN THE SELECTED AREAS BEING CARRIED OUT ABOVE THE DECOMPOSITION POINT OF SAID INCLUSION COMPOUNDS TO CAUSE THE RELEASE OF SAID GUEST MOLECULES AND THEREBY DISRUPTION OF THE FILM-FORMING MATERIAL TO FORM THE IMAGE IN THE COPYING MEDIUM.
 5. AN IMPROVED THERMOGRAPHIC COPYING MEDIUM COMPRISING A NORMALLY SOLID FILM OF ORGANIC RESINOUS FILMFORMING MATERIAL AND INCLUSION COMPOUNDS SUBSTANTIALLY UNIFORMLY DISTRIBUTED ADJACENT A SURFACE OF SAID FILM, SAID INCLUSION COMPOUNDS COMPRISING CLATHRATES FORMED OF CRYSTALLINE HYDROQUINONE HOST MOLECULES CONTAINING CARBON DIOXIDE GUEST MOLECULES, SAID CLATHRATES BEING DECOMPOSED BY HEAT TO RELEASE THE CARBON DIOXIDE GUEST MOLECULES FROM THE CRYSTALLINE HYDROQUINONE HOSE MOLECULES, AID CARBON DIOXIDE GUEST MOLECULES BEING CAPABLE OF DISRUPTING SAID FILM UPON RELEASE FROM THE CRYSTALLINE HYDROQUINONE HOST MOLECULES, SAID FILM COMPRISING A SYNTHETIC THERMOPLASTIC VINYLIDENE CHLORIDE POLYMER AND IS DISPOSED AS A SOLID COATING ON THE SURFACE OF A TRANSPARENT SYNTHETIC POLYMERIC SUBSTRATE HAVING A HIGHER SOFTENING POINT THAN SAID FILM. 